The present invention relates to RF power amplifiers, and more particularly to an output correction circuit which provides closed loop continuous amplitude and phase correction of solid state amplifiers.
An example of this application is for a solid state phased array requiring thousands of very accurate (say .+-.5.degree. phase .+-.1/2 dB amplitude) power amplifiers in order to produce very low sidelobe transmit patterns.
Most conventional solid state phased arrays have been concerned with power output, cost, and efficiency. The poor output accuracy of solid state phased arrays, i.e., the amplitude and phase errors relative to an ideal distribution, was accepted as the nature of the solid state approach. The present invention is particularly suitable for the class C amplifiers normally employed below S band. For these amplifiers, changing drive level may be a very difficult way to adjust the output because the input/output relation is non-linear and very sensitive. Also the amplitude and phase are not independent. One known method for controlling linear class A amplifiers is described in "Adaptive Module Techniques," A.W. Morse and G.S. Hill, Final Report to RADC, Griffiss Air Force Base, RADC-TR-83-98, June 1983. The drive level is changed in this approach. Separate measurements of amplitude and phase are made, a relatively complex procedure. Also the method is not closed loop; consequently, accurate phase and amplitude measurements are necessary. These measurements usually involve the use of accurately matched or accurately calibrated active devices (detectors, amplifiers, or the like).